When a Web server responds to an HTTP request, the response typically consists of a status line, some response headers, a blank line, and the document. A typical response looks like this −
HTTP/1.1 200 OK Content-Type: text/html Header2: ... ... HeaderN: ... (Blank Line) <!doctype ...> <html> <head>...</head> <body> ... </body> </html>
The status line consists of the HTTP version (HTTP/1.1 in the example), a status code (200 in the example), and a very short message corresponding to the status code (OK in the example).
Following is a summary of the most useful HTTP 1.1 response headers which go back to the browser from the web server. These headers are frequently used in web programming −
Sr.No. | Header & Description |
---|---|
1 | Allow This header specifies the request methods (GET, POST, etc.) that the server supports. |
2 | Cache-Control This header specifies the circumstances in which the response document can safely be cached. It can have values public, private or no-cache etc. Public means document is cacheable, Private means document is for a single user and can only be stored in private (nonshared) caches and no-cache means document should never be cached. |
3 | Connection This header instructs the browser whether to use persistent HTTP connections or not. A value of close instructs the browser not to use persistent HTTP connections and keep-alive means using persistent connections. |
4 | Content-Disposition This header lets you request that the browser ask the user to save the response to disk in a file of the given name. |
5 | Content-Encoding This header specifies the way in which the page was encoded during transmission. |
6 | Content-Language This header signifies the language in which the document is written. For example, en, en-us, ru, etc. |
7 | Content-Length This header indicates the number of bytes in the response. This information is needed only if the browser is using a persistent (keep-alive) HTTP connection. |
8 | Content-Type This header gives the MIME (Multipurpose Internet Mail Extension) type of the response document. |
9 | Expires This header specifies the time at which the content should be considered out-of-date and thus no longer be cached. |
10 | Last-Modified This header indicates when the document was last changed. The client can then cache the document and supply a date by an If-Modified-Since request header in later requests. |
11 | Location This header should be included with all responses that have a status code in the 300s. This notifies the browser of the document address. The browser automatically reconnects to this location and retrieves the new document. |
12 | Refresh This header specifies how soon the browser should ask for an updated page. You can specify time in a number of seconds after which a page would be refreshed. |
13 | Retry-After This header can be used in conjunction with a 503 (Service Unavailable) response to tell the client how soon it can repeat its request. |
14 | Set-Cookie This header specifies a cookie associated with the page. |